The 29-year-old Spearmon tested positive for Methylprednisolone during an international track meet on July 6 in Edmonton, Canada.
Spearmon claimed the anti-inflammatory drug was in a prescription he was taking and that he didn't know that it was on USADA's and the World Anti-Doping Agency's banned list.
Spearmon could have asked for a therapeutic exemption to continue taking the drug but failed to do so.
"After a thorough review of the case, including Spearmon's medical records, USADA has accepted Spearmon's explanation that the Methylprednisolone was not being used in an effort to enhance his performance," USADA said.
Spearmon took fourth place in the 200 metres final at the 2012 Olympics in London.
He reached the semi-finals of the 2013 World Championships in Moscow. His personal best for 200m is 19.65sec.